My Toro lawnmower featuring a Briggs-Stratton 7.25HP motor has been losing power lately. It is about 2 years old and I've used the maintenance kit (spark plug, air filter, oil, & fuel treatment) to prep it at the start of each year. This year, it has really been struggling however. Typically, when I start it up, it oscillates between running strong and puttering out a few times before it's either ready to go or putters out completely. These symptoms have gotten progressively worse until it won't start at all.

I used a carb cleaner a few weeks ago, which really helped to get it going again but the problems came back a few weeks later and additional carb clearner doesn't seem to be helping anymore. This past weekend I bought another maintenance kit for it but it still won't start at all.

It may be of significance that I think I may stress it a bit with cutting tall sometimes wet grass as well as with taking it around my very uneven back yard.

1 Answer
1

This is a carburetor issue, most likely caused by ethanol gas. Ethanol laced gas reeks havoc upon small engines. The easiest fix for it is to purchase a new carburetor for it, due to paying the price for a replacement carb outweighs the cost in time and frustration which will be brought upon you trying to rebuild it. I have tried to rebuild small engine carbs in the past with only limited success. Besides the cost of the rebuild kit, you will still have to take your time to get it running, if it ever will. New ones are relatively cheap online and very easy to obtain, especially for B&S engines. In the future use a product such as Sta-Bil which will treat the gas and make it so it won't do this again. Sta-Bil is a gas stabilizer which will keep the gas usable for up to two years. Without it, the gas is only good for about 30 days. The way it works is by not allowing the ethanol to absorb moisture from the air. The ethanol/water mixture is what causes the carbs little orifices to plug up and is near impossible to clean out without extraordinary means.

I took the carburetor completely apart and it doesn't look visibly dirty. Would the damage be noticable? The valves and mechanisms all seem to actuate freely. I put it back together and the lawnmower still doesn't start at all. For all I can tell, it's not even getting a spark now.
– kjgregoryJul 26 '14 at 16:41

@user2635036 ... The problem lies in that when the ethanol absorbs water, it gets stuck in the little ports and bleeds. You won't see it, but they are plugged. The mechanical portions of the carb will probably work just fine.
– Pᴀᴜʟsᴛᴇʀ2♦Jul 27 '14 at 0:00

2

Turns out I was right about it not getting a spark. I didn't notice that the new plug I put in had the electrode & anode mashed together. I adjusted the gap and it went back to starting & sputtering. I then followed a youtube video explaining out how properly clean the carburetor. Now she's running strong :-)
– kjgregoryJul 27 '14 at 20:33